Building structures are known having rigid structural members which are spaced apart to support enclosure sheets for the buildings. The enclosure sheets may be panels extending between structural members, but other sheets such as transparent sheets for greenhouses, are used. In some cases, the enclosure sheets are provided by transparent flexible sheet material extending from structural member to structural member. Such arrangements are shown in various patent specifications. For instance in EP A 0106920, a building canopy system is shown comprising hollow sleeves of polyethylene or polyester which are fastened by their edges to beam sections supported by upright columns and the space within the sleeves needs to be pressurized. The structural members are each provided with concrete foundations to support them separately in the building structure.
A similar type of arrangement is described in U.S. Pat. No. 5,210,983 which discloses a greenhouse which has two spaced apart enclosure sheets of polyethylene foil supported by a structure comprising uprights interconnected by steel wires.
A further structure for supporting two spaced apart enclosure sheets is described in U.S. Pat. No. 4,665,670. The structure requires a clamp to have both enclosure sheets clamped at the same location and because of this closeness of the sheets at the clamping position, air pressurization is required between them to hold them apart so as to provide the benefits of dual insulation. Of interest also are U.S. Pat. Nos. 5,076,033, 5,044,131 and 5,224,306, each of which relates to a single covering sheet extending across rigid supports. In U.S. Pat. Nos. 5,044,131 and 5,076,033 the enclosure sheet material needs to be assembled to the structural members simultaneously with erection of the structure itself.
None of the above described patent specifications is concerned with structural members for buildings which enable a completed structure to be made cheaply, simply and quickly and in finished form before enclosing the structure with two enclosure sheets spaced apart in face-to-face relationship. In addition to this, the above described structures tend to be overly complex--and a varied amount of parts are required to make a building.